No one has attempted to determine the precise time during germ cell formation at which the cells attain the potential to meet the essential energy demands which will be thrust upon them after ejaculation. We propose to investigate this question by: a. Isolating germ cells representing several developmental states from the rabbit and analyzing them for key enzymes of metabolic pathways as well as for their rate of ATP turnover. This will indicate whether changes in enzymatic content occur during formation and development. b. Characterizing the mode of sugar transport in pre- and post-epididymal bovine sperm cells. The energy requirements of ejaculated sperm from humans and lower mammals are apparently met by sugar metabolism. Since few differences exist between the glycolytic enzymes of sperm and host tissue, characterization of the sugar transport system may provide information necessary to design a chemical agent to disrupt sperm metabolism without altering host cells. c. Characterizing the energy demands of human, bovine and rabbit ejaculated sperm. These studies will focus on factors which control ATP turnover. The ultimate experimental study, isolation of human germ cells at various stages of development and characterization of their energy metabolism, is not feasble. Careful characterization of energy metabolism in rabbit germ cells representing several developmental states plus continuing our studies on the metabolic characteristics of pre- and post-epididymal bovine sperm may provide a model for human germ cell energy metabolism. Concomitant studies of rabbit, bovine and human ejeculated sperm should provide a comparison of energy metabolism in these cells. Extrapolation of the developmental profile from lower mammals to humans is difficult. However, characterization of the cells from several animals in he same laboratory can eliminate much uncertainty in the comparison.